Hydraulic synchronizing system



June 19, 1951 H. J. NlcHoLs HYDRAULIC SYNCHRONIZING SYSTEM 4Sheets-Sheet 1 Filed June 6, 1949 June 19, 1951 H y, NlcHoLs 2,557,679

HYDRAULIC SYNCHRONIZING SYSTEM Filed June e, 1949 4 sheets-Sheet z J5 61Ja El 251/ f3 62 INVENTOR BY Mmw ATTORNEY June 19, 1951 H. J. NlcHoLsHYDRAULIC sYNcHRoNIzING SYSTEM Filed June e; 1949 4 Sheets-Sheet 3mvNToR J MCA/01,5,

ATTOR Y H. J. NICHOLS HYDRAULIC SYNCHRONIZING SYSTEM June 19, 1951 FiledJune 6, 1949 4 sheets-sheet 4 INVENTOR" MJ Maf/046 ATTORNEY PatentedJune 19,. "1951 UNITED STATES PATENT OFFICE 2,557,679 HYDRAULICsYNcHRoNTzING SYSTEM Harry J. Nichols, Point Pleasant, N. J. ApplicationJune s, 1949. serial No. 97,462 17 claims. (o1. 17o-135.29)

This invention relates to an improved method and apparatus forautomatically synchronizing rotary machinery and has particularreference to the synchronizing of prime movers such as the engine orengines of an airplane, marine vessel, or power plant, especially wheresuch prime movers have speed regulating means under hydraulic Thisapplication is a continuation in part of my application Serial No.523,301 filed February 21, 1944, now abandoned.

A principal object of the invention resides in the provision of a novelsynchronizing method utilizing timed hydraulic impulses for comparingthe Speed of one or more engines with a master Speed and forautomatically correcting the speed of any engine which is out ofsynchronism with the master speed thereby to bring it into synchronismwith the master speed and thereafter to maintain synchronism therewith.

Another principal object is to disclose suitable and practical apparatusof known types for implementing the novel synchronizing method of theinvention.

Another object is to disclose apparatus for implementing the novelsynchronizing method adaptable for manually or automaticallysynchronizing one or more engines, either by varying the load thereonindependently of the throttle adjustment or by controlling the fuelinput thereto.

Another object is to provide improved auto- -matic synchronizerapparatus of the utmost simplicity and reliability which is small insize, light ,in weight, and low in initial installation and vmaintenancecosts.

Another object is to provideA a speed control system whereby thecentrifugal speed governors commonly used on engines of the classdescribed may be eliminated and the engine placed under the control of amaster speed device which remains unaffected by the engine load.

A further object is to provide versatile synchronizing apparatus whichis readily applicable `to various types of engines and other prime mov-`ers without requiring special provisions in the design, construction,or accessories thereof.

Other objects and advantages will be in part 'obvious or become apparentas the invention is .more particularly hereinafter pointed out.

In the accompanying drawings, in which like ireference numerals are usedto designate Similar z-or corresponding parts throughout, there isillus- .itrated by way of example various manners of '"applying thevimproved method and suitable ap- Y Y Y 2 paratus therefor. Thedrawings, however, are for the purpose of illustration only and are notto be taken as limiting the scope of the invention as set forth in theappended claims.

Fig. l is a schematic diagram-fof the improved synchronizing apparatus.

Figs. 2 and 3 show in elevation and plan views, respectively, thedetails of the rotor of the rotary synchronizing valves shown in Fig. 1.

Fig. 4 is a diagram showing schematically the operation of the rotor ofthe synchronizing valve.

Fig. 5 is a detail of the pulsing valve shown in Fig. 1 illustrating theposition which the rotor assumes on stopping.

Fig. 6 shows an alternative arrangement of the manual control valves inthe system shown in Fig. 1. y

Fig. 7 is a schematic diagram illustrating an- ,other embodiment of themethod of the inven- ,ing yet another embodiment of the method of theinvention.

Referring to Fig. 1 of the drawings in detail, the numerals l0 and Ilindicate generally two engines which have been illustrateddiagrammatically by way of example as the engines carried by a twoengine airplane. Each engine drives a controllable pitch propeller, asindicated at l2 and i3. The pitch of each of the propellers is varied bya pitch changing mechanism, as indicated generally at I4 and l5, whichmechanism is provided with hydraulic control means. The pitch changingmechanism and hydraulic control means may be of the construction shownin my U. S. Patent No. 2,423,400 issued July 1, 1947.

It is thought sulcient for the purposes of this disclosure to state thatwhen hydraulic fluid under pressure is supplied to the conduitsdesignated C" and F, respectively, the pitch chang- -.-ing mechanismrotates the Vpropeller blades axially to coarsen or to fine the pitch.It is of course well known thata coarse pitch tends to ,increase theengine load and to decrease the vthe throttle of the engine to thedesired power output.

The principal elements ofthe synchronizing `system illustrating oneembodiment of the invention comprise a source of hydraulic fluid under@regulated pressure, as for example a tank I6 vand a gear pump `Il, withpressure relief valve I8;

a master speed device 20, as for example, an electric motor, with asettable speed governor (not shown); a rotary hydraulic pulsing valve40, or equivalent, driven by the master speed device 20 and functioningtherewith as a periodic impulse generator and rotary speed setter; and arotary hydraulic synchronizing valve, or equivalent, as for examplevalves 50, 5l, driven by each controlled engine and functioning as aspeed comparator and speed regulator; and accessory conduits and valvesfor connecting the elements of the hydraulic system and for regulatingthe supply of hydraulic fluid to the hydraulic controls.

An important accessory element of the illustrative system of theinvention is the safety clutch device 30 coupling the master speeddevice 20 to the pulsing valve 46 which acts to disconnect the pulsingdevice from the master speed device in the event the speed of the masterfalls below a predetermined value, or exceeds another predeterminedvalue. The pulsing valve 4U acts t cut off the supply of hydraulic fluidto the synchronizing valves 50, l in such event, thereby to place thepropellercontrols in safe condition and solely under manual control.

A suitable form of master speed device is an electric motor equippedwith a speed governor with suitable settable means for adjusting thespeed to any desired rate within a predetermined range. Such governorcontrolled motors being well-known and in common use, detaileddescription herein is deemed unnecessary.

The master speed device 20 drives by means of a shaft 2| and acentrifugal clutch device 30, termed the automatic safety clutch, therotary pulsing valve, as indicated at 46. The pulsing valve is providedwith a rotor 42 housed in a. fluid tight casing 4| having two ports 43,45, the rst named connecting with the conduit I9 from pump I1, and thesecond to conduit 46 leading to conduits 41 and 48 connected with thesynchronizing valves 50, 5I respectively.

The rotor 42 is positively driven by safety clutch 3U at the speed ofthe master speed device 26 or in fixed ratio thereto. The port positions43, 45 and the cut away portion 44 of rotor 42 are so co-ordinated, asindicated in the diagram Fig.4 that during a small part of eachrevolution of rotor 42 hydraulic fluid from pump l1 has passage throughthe valve. Thus timed hydraulic pulses indicating the speed of themaster `speed device are provided to the operating circuits of thehydraulic system.

Each of the engines I0 and Il drives a rotary synchronizing valve, orequivalent, as indicated at 50, 5l, respectively, of identicalconstruction and connected by conduits 41 and 48 to conduit 46 carryingthe timed fluid pulses from valve 40.

Referring now to Figs. 1 to 4 inclusive, each rotary synchronizing valvemay comprise a fluid tight casing 52, and a disc shaped rotor asindicated at 53, the latter being positively driven at the speed of theassociated engine, or in fixed ratio thereto. Each casing 52 is providedwith a radial port 54 located at the median plane of the casing, and twolongitudinal ports located in the same diametral plane as middle port 54and extending from opposite sides of the casing 52, as indicated at 55and 56. Each rotor is closely fitted in its casing, except for twoarcuate channels 51, 58 cut in opposite edges of the rotor rim asindicated in Figs. 2 and 3.

Referring particularly to Fig. 4, which shows diagrammatically the rimof rotor 53 in linear Sii) development and in schematic relation to thethree ports of the casing 52, it will be noted that arcuate channels 51and 58 extend over a semi-circular arc and at their widest portion arecut into the rim of rotor 53 until only one third of the face remains.At two opposite points on the rim, indicated at 6l and 62, vanes arethus formed which separate the arcuate channels. It is obvious that wheneither of these vanes is passing the middle port 54. the ow of hydraulicfluid is checked, hence these relative positions may be termed cut-offpoints. At other rotor positions fluid can pass to one side port or theother Via the continuous channel. The vanes are shaped so that the flowof fluid is gradually reduced as the cut-olf points are approached.

The synchronizing valve acts both as a speed comparator and as a speedcorrector. Assume that the direction of rotation of the master speeddevice and the engine is clockwise as indicated by the arrows at thebottom of the diagram; also that at the moment the vane 6l covers themiddle or entrance port 54 coincident with the arrival of the timedfluid pulses from the pulsing valve 46. Thus for the moment, no speedregulation takes place. However, in the event the engine speed is fast,rotor 53, which rotates with the engine speed, will rotate relativelyclockwise thus moving to the right-as viewed in Fig. -and bring channel51 under entrance port 54 co-incident with the arrival of the timedpulses. So long as this situation continues, the timed pulses will passout port 55 and into conduit C, causing the propeller pitch controls toinitiate speed retarding action.

If, on the contrary, the engine speed is slow, rotor 53 will movecounter-clockwise, or to the left as seen in Fig. 4, whereupon channel58 will conduct the timed fluid pulses to port 56 and eventually intoconduit F thereby initiating speed regulation in the opposite sense fromthe first case, that is to accelerate the engine speed. Accordingly,channel 51 can be regarded as the Retardation initiator, while channel58 can be regarded as the Acceleration initiator. More extensiveanalysis will show that regardless of the assumed initial speedconditions, the synchronizing rotor will initiate the proper correctiveaction to bring the engine into synchronism with the master speeddevice.

Referring again to Fig. 1, the improved hydraulic apparatus describedoperates to regulate the speed of each engine to establish and maintainsynchronism of each engine with the master speed device in the followingmanner: For each rotation of the master speed device 26, the pulsingvalve 46 admits a pulse of hydraulic fluid under pressure to conduit 46and thence to conduits 4l and 4E. Assuming that engine I0 is runningfast relative to the master speed device 20, the rotor 53 ofsynchronizing valve 50 will rotate in leading phase relation and port 55will be uncovered by retarding channel 51 in communication with thatport, as indicated for engine I6, permitting the fluid pulses to enterconduit 65 and thence proceed to conduit C which controls the pitchchanging mechanism to coarsen the pitch, thereby increasing the load onthe engine and reducing the engine speed. When the engine speed isreduced below that of the master speed device, rotor 53 will rotate inlagging phase reiation, and the accelerating channel 58 will comeopposite port 54 coincident with the arrival of the fluid pulses, asindicated byvalve I of engine Il. Thereupon, the above described eventswill take place in vreverse to increase the engine speed. When theengine speed is regulated to that of the master speed device, theneutral vane 6l will cover the port 54 coincident with the arrival ofthe synchronizing pulses, terminating the corrective action for the timebeing, thereby establishing synchronism.

The improved synchronizing apparatus thus acts to compare the speeds ofthe master speed device and the engine and, when the speeds aredifferent, yto apply proper corrective control to bring the engine speedinto synchronism with that of the master speed device. As the controlledengine approaches synchronism, the neutral vane reduces the correctiveaction until it becomes nil when synchronism is established. Thesynchronizer apparatus thus automatically provides a correction rateproportional to the departure from synchronous speed, resulting insocalled dead-beat speed regulation. It will be noted that thesynchronizing system of the invention will produce exact synchronism ofeach engine with the master speed device, since any difference in speedis cumulative and will eventually be corrected. Obviously, additionalengines could be synchronized by a simple duplication of thesynchronizing apparatus which applies to the individual engine.

Referring again to Fig. 1 in connection with Fig. 5, it is to be notedthat the rotor 42 of pulsing valve 40 is hydraulically unbalanced, thatis, when the opening 44 comes opposite the entrance port 43 and beforeexit port 45 is uncovered, the pressure of the hydraulic Huid tends toforce the rotor 4,2 tothe opposite side as indicated by the arrow inFig. 5. As a consequence, when the rotor 42 is uncoupled from the masterspeed device by the double safety clutch as mentioned above, the rotor42 will naturally come to rest in the off-position A as shown in Fig. 4.This feature automatically renders the synchronizing systemnon-operative whenever the pulsing valve is allowed to come to rest,whereupon the pitch adjustment is solely under manual control.

Suitable manual control valves may be provided for each engine, as forexample the three-way rotary valves 10, 'H shown in the diagram of Fig.1,v to subject the engines to direct manual control of the propellerpitch independently of the usual throttle controls. Each manual controlvalve is preferably connected in the hydraulic circuits between thefluid source l'l and the conduits C and "F leading directly to thepropeller controls. These valves may be of well-known type in which arotary member F3 is actuated by a handle l5 to cut-off the fluid supplyor to divert it to one or the other of two conduits 'I6 and 'I1 leadingto the propeller control conduits C and F respectively. Each manualcontrol valve is thus eiective to cause actuation of the associatedpropeller to fine or coarsen the pitch of the blades,'

whether or not the synchronizing controls are in operation. With thisarrangement, the pilot can manipulate the manual controls to settheblades at any desired pitch at any time, such as for example, instarting up the engines or in emergencies.

Suitable manual hydraulic valves, of knownl type, as for example valve80, may be provided to enable the synchronizinghydraulic circuits to beturned on or shut 01T as desired.

f Referring to Fig. 6, which shows an alternative arrangement of themanual control valves, lines I9 and 46 may be connected by a 3-way valve80a (in lieu of valve 8D) and another 3-way valve. 80h

connected in line 46 as shown. With this ar rangement, by properlysetting valve h the synchronizing pulses may be applied by means ofmanual control valves 10, 'Il to either or both propellers, thereby toobtain a micrometric adjustment of the pitch for purposes ofsynchronization. By properly setting valves 80a and 80h pressure uid maybe supplied to valves 10, 'II-,as before.

, Finely adjustable valve means, as for example needlevvalves 8l 82, 83and 84 indicated in Fig. 1, may be provided to regulate the drainage offluid from the propeller hydraulic controls. These valves provide aready means of adjusting the rate of Ahydraulic action of thesynchronizing apparatus to be applied smoothly under various operatingconditions. This adjustment feature enables the synchronizing apparatusof the invention to be applied to a wide variety of sizes and types ofengines working under various load conditions with good results.

Referring now to Fig. 7 which shows generally and .schematically anotherembodiment of the synchronizing method of the invention, it is assumedfor purposes of illustration that the system to be synchronizedcomprises two engines, one under the independent control of anadjustable speed governor of known centrifugal type. Since therequisiteapparatus may consist of compoents of known types which may Vary indetails of construction, the system is shown schematically, thecomponents being arranged for convenience in illustration andnon-essential details of the apparatus being generally omitted.

Engine No. 1 is assumed to function as the master speed setting device,while engine No. 2 is assumed to function as the slave or followerengine, whose speed is so regulated to establish and maintainsynchronisml of the system as a whole. Each engine is illustrated ashaving an independent source'of hydraulic fluid, indicated generally bytanks TI, T2 and pumps PI, P2. The speed of engine No. l is assumed tobe under the control of an adjustable, constant-speed centrifugalgovernor which hydraulically actuates the pitch changing mechanism, asfor example that shown and described in U. S. Patent No. 2,392,364 to F.W. Caldwell et al., issued Jan. 8, 1946. It is to be expresslyunderstood however that the method described can be .applied to othertypes of engines and prime movers employing hydraulic governors whichgctuate throttles, fuel injectors, Aand other means 4whereby the speedthereof can be regulated. As will become evident, other engines could beadded to the system and, by application of the method of the inventionand mere duplication of the apparatus illustrated, can be synchronizedwith the master engine in the same manner as engine No. 2.

In Iapplying the method of the invention, engine No. l, as the masterspeed setter, maybe provided with a device, generally termed an impulsegenerator IG, for generating timed fluid impulses each indicative of themaster speed. This device comprises essentially a cam-driven smallplunger 63 ywhich .works tightly in a, miniaturecylinder so as togenerate a pressure wave or impulse in an impulse transmission line,-indicated generally at d6, upon each quick stroke of the plunger. Thecam 64 may have a single lobe, las shown, and may be rotated by a driveshaft 6l! at engine speed, in which case each timed -impulse representsone revolution of the engine, or

it may be driven at some fixed ratio to the engine speed, say athalf-speed. Animpulse generator suitable forv` present purposesis=describedin U Si Patenti No.. 1,372,944i to1G':vGonstantinescosissued March29, 1921. The line 46Lshouldibe-keptlunderlhydraulicl pressure, andi is connected to .the pressure lineaofthegovernor for that` purpose, as shown.

Engine No.- 2, representing any follower' engine;- may beprovidedf.'withAA an impulseresponsive device 40a, generally termed an impulsemotor, whichin` this case actuates avalve plunger 4.2ararrangedso as toproduce-a timed fluid pulse in=V a local hydraulic line leading to thesynchronizingvalve as describedlhereinafter; This device comprisesessentially a spring-opposed valve plunger 42aworkingtightlyy inaminiature cylinder as shown. The plunger spring should bestrong enoughto hold the valve-plunger-42'a in-closed position against thenormallpressurein the impulse transmission line 4S. An' impulse motoradaptable'for present purposes is described inthe Constantinescopatentcited above;

Engine No; 2 mayalso be provided with a reciprocating valve 5la of knowntype, functioning as a synchronizing; valve, whichmay be-driven by acamEl4 mounted on a drive shaft36 driven at the same speed ratio as theimpulse generator; As shown, thek synchronizing valve plunger 53a isdriven by anv eccentricy cam; and hence. makes one reciproca-tion foreach revolution of its drive shaft 60.

A locking valve LVof known type', is connected' in the hydrauliccircuit, between the synchronizingvalve and the lines C and F leading tothe propeller, thereby normally to isolatethese portions of thevhydrauliccircuits, as is lwell understood.

Theoperation ofthe arrangement described is as follows: It is assumed'that the two engines arev running and that.. their speeds have beenregulated to parity by adjusting their throttles,

that is, the engines have` been adjusted to approximately the same speedbut not to an exact synchronous. speed. Further, it is assumed that atimed'. impulse has just been transmitted.i and received,.and thesynchronizing valve- Bla is in mid position. Under these assumptions theinstantaneous position of. valve 51a could indicate a condition ofsynchronism, or that the follower engine was lagging or leading by aneven nmnber of revolutions.

If it be assumed that engine No. 2'- is leading, onv followingrevolutions cam 61' will gradually advance clockwise as indicated by thearrow, relative to the successive openings of pulsing valve de.; andconsequently local hydraulic pulses, corresponding to the received timedimpulses, will be admitted by synchronizing valve Sla to; the, top-halfof the lock valve LV. Responsively thereto, the iioating plunger of thelock valve will open line F to exhaust and'simultaneously the localpulses will enter line C, thereby coarsening the pitch by. smallincrements. Illhiscoarser pitch will gradually slow down engine. No. 2,causing an eventual establishment .of true synchronism, with the systemagain functioning in the condition illustrated.

If, conversely, it has been assumed thatengine No. 2 was lagging,synchronizing valve 51a would gradually open in the other directionrelative to the timed pulses, thus admitting local pulsesto the lowerhalf ofglock valve LV. This wouldlcause line C to be openedto;exhaustand local: pulses toebe admitted. to linev E; thereby finngthepitch and causingthe engine tospeed up,

again causing.` anl eventual establishment of. true synchronism.

It should be-.noted1that the synchronizing action is4 responsive to thephase of the follower relative to that .of the master. Thesynchronizingactionthuslamounts .to regulating .the phaseof the followerto conform-with that of the master, andwill occur. at vany speed-towhichthe governorI offthemaster. enginemay ber-adjusted; thesy-nchronizingfmeansfacting to makeup any differences between theactualvspeeds of the two engines.

Assuming I synchronism has been. established'A as described, av changeofrelative phase will precede any changelofspeed to .which the governor ofthemaster engine would be responsive, hence the synchronizingaction isvinherently more sensitive-thanV the governor action. It follows .that agovernor vof 'low sensitivity and-high stability may be employed toregulate the speed of themaster engineV with practical advantages wellknownin the art, yetgaccuratesynchronization ofthe slave engine will' bemaintained during variations-in the speed of the master engine.Furthermore, once synchronismisV established any momentary differencesin speedwill be made up, hence the average speedsof `the two engineswill be exactly equal; Moreover, a uniform phase relationwill bemaintained, and in practice this relation can be adjustedjto minimizevibration effects, in wellknown manner.

Av 3-way valve. 30e mayv be connected in the hydraulic circuits asshown, and by manipulatingrthis valve, synchronizing pulses may beapplied to the propeller driven, by engine No. 2-as desired, as forexample in starting upor for pur- Doses of. manual synchronization asVbefore described,

Referring now to Fig. 8 which shows generally and, schematically anotherembodiment ofthe methodof theinvention', inthis case it is assumed byway of. example that twoV engines are toA be employed `for driving two.independent generators connected in parallel in an alternating currentsystem. Insuchapplicationaboth engines are required; to run. at the.same synchronous speed.` thereby, tol maintain. a predetermined.constant frequencyA ofthe generated current. Asis well understood,ordinary centrifugal governors are unable tol maintain a constant. speedin. such systems, because the. speed set by the governors varieswiththeload, due tothe speed droop characteristic. It will. now be explainedhow. the method. of the. invention can be applied tosupplement. theaction of centrifugal speed. governors, so ,as to maintain aconstant-frequency in an A. C.,system.

Itis assumed. that each of thetwo engines is equippedrwith an adjustable-speed hydraulic governor, SGI ofY known type, which; governorscon,- troll thefuel` supplied to the engines in wellknown manner asindicated schematically. The mainfunction ofV each governor is tomeasure the speedof the engine, andfto regulate the fuel so asttomaintain a substantially constant speed during sudden loadvariations.Since the governors are.l capableV ofV continuous action, while thesynchronizing, means is capable only ofintermittent actionit, can be.assumed. thatthe governors can override the synchronizing action ineventof sudden. and large changeset load. As indicatedrschematicallythegovernors each con.- trol apilotvalvezplunger VP-which in turnlconrtrois; the admission, of;Y pressure oil; to. a. power piston PP whichregulates a fuel valve supplying the engine.

A master speed setter, which may take the form of a synchronous motor SMsupplied with A. C. at the desired frequency from an external source,drives two impulse generators IG, as in the first example. Each enginemay be provided with an impulse motor driving a pulsing valve 40a, asynchronizing valve 59a, Sla and a lock valve LV, these being connectedhydraulically to actuate the power piston PP, as indicated. Each powerpiston is therefore under the joint control of the governor and thesynchronizing means.

As before it is assumed that the governors have been adjusted toapproximately synchronous speed and the control elements are inmid-position, indicating either a condition of synchronism, or aninitial lead or lag due to lack of precise accuracy in the governorsettings.

If it be assumed that engine No. 1 is leading, cam S1 will advanceclockwise relative to the arrival of the synchronizing impulses, whichindicate the synchronous speed, and consequently the synchronizing valve50a will admit synchronizing pulses to the top half of the lock valveLV, the floating plunger of which will open the lower check valve,permitting fluid to escape from the underside of power piston PP,v thusreducing the fuel supply to the engine. Engine No. 1 will thereforegradually slow down until it runs at the synchronous speed, whereuponthe hydraulic elements will be restored to neutral position, asillustrated.

If it be assumed that engine No. 2 is lagging, cam 61 will movecounterclockwise relative to the arrival of the synchronizing impulses,and consequently synchronizing valve Ela will admit synchronizing pulsesto the lower half of lock valve LV', and thence to the bottom of powerpiston PP. Power piston PP will thereby be gradually raised, admittingmore fuel to the engine and increasing its speed to synchronous speed.

It is well understood in the art of governors that the relative loadsassumed by two engines driving parallel connected alternators willnormally depend upon the droop characteristics of the governors.However, it is to be noted that in the present embodiment of the methodof the invention, the position of the power piston PP and hence of thefuel valve can be varied by the synchronizer means Vindependently of thegovernors. It follows that the load division is no longer dependent uponthe droop characteristics of the governors, but can be adjustedindependently of the governors. Manual 2-way valves l0, 1| may thereforebe connected in the hydraulic circuits as shown to enable an operator toadjust the load division as desired. To facilitate this, loadindicators, not shown but of known type, may be employed to advantage.

In summary, it is to be noted that in each embodiment of the method ofthe invention, definite information indicative of the master speed isintroduced into the speed control system by means of timed hydraulicimpulses. The general method thus comprises the steps of producing aseries of timed hydraulic impulses indicative of a master speed, andutilizing these impulses to compare the speed of an engine with themaster speed and to applycorrective speed control measures to an enginewhich may be out of synchronism with the master speed.

[While certain arrangements have been illustrated in the accompanyingdrawings and hereinabove described for the purpose of disclosing theinvention, it is to be understood that the invention is not limited tothe particular arrangements described, but that various changes in thecomponent parts and arrangement of these parts may be resorted to withinthe scope of the subjoined claims.

Having now described the invention so that others skilled in the art mayclearly understand the same, what it is desired to secure by LettersPatent is as follows:

I claim:

l. Hydraulic apparatus for synchronizing the propeller driving enginesof a multi-engine aircraft, each engine having means responsive tohydraulic fluid under pressure to control its speed, comprising, arotary master speed device for providing a reference speed, a pumpconnected therewith supplying hydraulic fluid under pressure, rotaryhydraulic valve means driven by said master speed device and connectedin the output channels of said pump for generating timed hydraulicimpulses representative of the speed of said master speed device, androtary hydraulic valve means driven by each engine for comparing theengine speed with the reference speed and for applying correctivehydraulic pressure to the responsive speed control means.

2. Hydraulic apparatus for synchronizing the speed of an engine with thespeed of a master speed device comprising hydraulic control means forvarying the load on the engine, an hydraulic impulse generator driven bysaid master speed device, an hydraulic valve device having a portionrotatable at engine speed, and means for utilizing impulses from saidimpulse generator to compare the engine speed with the master speeddevice and to vary the adjustment of the speed of the engine inverselyto and proportionally to the difference in speed between the engine andthe master speed device.

3. Hydraulic apparatus for synchronizing the speed of engines comprisinga master speed device for establishing a reference speed, an enginespeed control for each engine, hydraulic adjusting means for each enginespeed control, an. hydraulic impulse generator driven by each engine,hydraulic valve means including a rotatable portion driven at enginespeed for utilizing timed impulses from said impulse generator tocompare the engine speed with the reference speed and to applycorrective adjustments to the engine speed controls inversely andproportionallylto the difference in speed between the engine speed andthe reference speed.

4. In hydraulic apparatus for synchronizing a plurality of prime moversone of which is equipped with hydraulic control means and the other witha timed hydraulic impulse generator, rotary hydraulic valve means forcomparing the speed of the prime movers and for applying correctivehydraulic control to the one of said prime movers equipped withhydraulic control rneans` which is out of synchronism to adjust thespeed of said prime mover to conform with the speed of the other primemover.

5. Means for controlling and synchronizing the speed of an engine with asettable master speed device, said engine driving a controllable pitchpropeller having hydraulic means for controlling the pitch of saidpropeller, a hydraulic fluid pump, means controlled by said master speeddevice for producing impulses in the output iiuid of said pump timedproportionally to the speed of said master speed device, a hydraulicdevice lli driven proportionally tof the speed of, said engine forutilizing said impulses to compare the speed of said engine With that ofthe master speed device and for actuating the hydraulic control. meansof its associated propeller to correct any speed difference between saidengine and said master speed device, and uid conduits for operativelyconnecting the aforesaid hydraulic elements.

6. Hydraulic apparatus for synchronizing the speed of an engine withthat of a reference speed comprising hydraulic means for controlling thespeed of said engine, means for producing timed hydraulicimpulsesindicating said reference speed, a rotary hydraulic valve drivenpropor-1 tionally to the engine speed for comparing the engine speedwiththe reference speed and for automatically actuating said hydraulicspeed control means so as tocorrect any speed difference, and huidconduits for operatively connecting the aforesaid hydraulic elements.

7. In combination with an engine having hydraulic speed regulating meansassociated there with, hydraulic synchronizing apparatus com prising anhydraulic impulse generator, a master device for controlling saidimpulse generator to produce timed hydraulic impulses indicative oi thespeed of said device, hydraulic valve means operatively associated withsaid speed regulating means and said impulse generator for comparing thespeeds of said engine and said master device and for initiatingtheautomatic correction of any difference in the speed of said enginefrom the speed of said device.

8. In combination with the combination of claim '7, means forAregulating manually the said hydraulic speed regulating meansindependently of said synchronizing apparatus.

9. In apparatus for synchronizing the speeds of a plurality of engines,the: combination including a master speed setter, means forv producingtimed hydraulic impulses indicative of the speed of said master speedsetter, meansV for utilizing said impulses to compare the engine speedswith the master speed, and meansfor controlling the speeds of saidengine in` accordance with the comparison soas to correct thev speed ofan engine whichmay be out of synchronism with the master speed setter.

10. In apparatus for synchronizing the speed of a plurality of engines,the combination including a master speed setter, means for producing aseries or timed hydraulic impulses indicative of the speed of saidmaster speed setter, means for utilizing said impulses to compare theengine speeds with the master speed, and means for applying. correctivehydraulic speed control measures to any of said enginesJ which may beout of synchronism with the master speed setter as determined. by thecomparison..

l1. In. apparatus for synchronizing the speed of an engine with respectto the speed. of a master speed setter, the combination which includesmeans for transmittingaseries of. timed hydraulic impulses indicative.of the. speed of said master speed setter, means for utilizing saidimpulses to compare the engine speed with the master speed, and meansfor varying the engine speed in accordance with the comparison so as tocorrect any speed difference.

l2. In apparatus for synchronizing the speed of an independently drivenrotating element with respect to a reference rotary speed, thecombination. which comprises means for generating a series of timedhydraulic impulses indicative of said reference speed means fortransmitting said impulses to said rotary element, means for utilizingsaid impulses to compare the timing of said impulses with the speed ofsaid rotating element, and means for utilizing such comparison toregulate the speed of said rotary element in such manner as to establishand thereupon, maintain synchronism ofthe speed of said rotating elementwith said rotary speed.

13. In apparatus for synchronizing the speed of an independently drivenrotating element with respect to a reference' rotary speed, thecombination which comprises means for generating a series of timedhydraulic impulses indicative of said rotary speed, means fortransmitting said series of impulses for utilization at said rotating:element, means for utilizing said impulses. tu. compare the speed of therotating element with the reference speed, and means fory regulating 1the speed ofthe rotating element inv accordance with the comparisonthereby to establish and maintain a predetermined ratio between saidspeeds.

14. In a synchronous mechanical system comprising a master speed setterand a plurality of engines equipped with speedy regulating means,apparatus for synchronizing the speeds of any of the engines with thatof the master speed setter which includes means. for generating periodichydraulic impulses indicative of the speed of the master speed setter,means for transmitting said impulses to said engines, means forutilizing said impulses to compare the speed, of each of the engineswith that of the master. speed setter, and means for regulating thespeed or any engine out of synchronism with the master speed setter insuch manner as to establish and thereupon maintain it in synchronismwith said master speed setter.

15. In a system' for synchronizing the speeds cf a plurality of engines,each equipped. with speed regulating means, with that of a master speedsetter, the combination of means for generating periodic hydraulicimpulses indicative of the speed of said master speed setter, means fortransmitting said impulses to points of utilization, means for utilizingsaid impulses to compare the speed of each of the engines with that ofthe master speed setter, and means for regulating the speeds of theengines in accordance with the results of the comparison to establishand maintain synchronism with the master speed setter.

16. Apparatus. for synchronizing the speed of a prime mover with respectto a reference speed having, in combination, means for regulatingl the,speed of said prime mover, means for generating timed hydraulic impulsesindicative of thev reference speed, means for transmitting saidhydraulic impulses, means for receiving said hydraulic impulses, meansoperatively associated with said means for receiving said hydraulicimpulses and said means for regulating the speed of' said prime moverfor comparing the prime mover speed with the reference speed, and meansfor correcting the prime mover speed in accordance with such comparisonso as to establish and maintain a predetermined synchronous rela-- tionbetween the prime mover speed and the reference speed.

17. In combination with the. combination4 of claim 16, means forcontrolling the speed, of said 13 prime mover independently of saidsynchronizing apparatus.

HARRY J. NICHOLS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,154,785 Lemp Sept. 28, 19151,841,157 Seeger Jan. 12, 1932 Number

